Such approaches work by detecting an analog signal of a tank filling level sensor. The signal is sharply filtered through algorithms implemented in a control unit in order to reduce the sloshing in the signal caused by driving. Since the characteristic constant of the low-pass filter must be large, the low-pass filter becomes slower. The filtered signal will not indicate the prevailing filling level but instead will indicate a previous filling level. This is noticeable in particular when the liquid is being pumped out of the tank, as in the case of a fuel tank or an ADBLUE (a trademark as described below, also known as a diesel exhaust fluid or AUS 32) tank.
In addition, there are complex methods which attempt to increase the reliability of the low-pass filter result by taking into account the vehicle state (acceleration, braking, maintaining speed, stopping, etc.). Other methods use a second low-pass filter, which is faster than the first. This second low-pass filter should supply more up-to-date information about the filling level but its area of use is limited to vehicle states in which the sloshing turns out to be lower.
Other methods subtract the accumulated spent setpoint quantity of fuel in the case of a vehicle tank or the accumulated metered setpoint ADBLUE quantity in the case of an ADBLUE tank from an initial filling level during the sloshing phase to ascertain the filling level. The initial filling level should be measured by the filling level sensor in a “resting” phase. Each time the vehicle is in a “resting” phase, the initial filling level is measured again and the accumulated setpoint quantity is set to zero. This method relates to the desired quantity or the quantity to be injected or the quantity to be metered since the actual quantity injected is unknown due to tolerances, drift, aging, etc. This results in a deviation in the actual tank filling level, which increases over time and may be reset in the next “resting” phase.